Physiological Characteristics and Composition of Soleus Muscle Grafts of Rats (Exercise, Degeneration/Regeneration, Muscle Transplantation).

The grafting of skeletal muscle is used clinically for restoration of structure and function to areas of the body that have incurred major damage and loss of viable soft tissue. Following grafting, skeletal muscle fibers degenerate and then regenerate. Stable muscle grafts have a decrement in maximum tension development compared to control muscles, even after accounting for their reduced mass and cross-sectional area. This suggests that muscle composition is altered following grafting. Soleus (SOL) muscles from female Wistar rats were used for the present studies. Nerve-implant grafting operations and muscle dissections were performed while rats were anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Variables measured included contractile properties, morphology, tissue composition, and myofibrillar ATPase activity. At 56 d after grafting data were obtained from SOL grafts and control SOL muscles from sedentary, and from sprint and endurance conditioned rats. Conditioning by running began 28 d postgrafting and lasted for 28 d. Exercise conditioning did not affect any of the variables that were measured. Maximum tetanic tension of grafts was 66% of control value. For grafts, inulin space was 135%, total protein 93%, connective tissue protein 177%, and muscle density 99% of control values. Compared to control SOL muscles, the magnitude of decrement in maximum tension per cross-sectional area of SOL grafts was consistent with the differences measured for tissue composition. The hypothesis was tested that the relationship between maximum shortening velocity (fiber lengths/s) and myofibrillar ATPase activity observed in control SOL muscles would persist in SOL grafts. At optimal functional length, muscle length of grafts was 91%, yet fiber length was 127% of control values. The maximum shortening velocity of grafts was not different from control muscles, nor were angles of pinnation or sarcomere lengths. Myofibrillar ATPase activity of grafts was 65% of control values. The similarity of maximum shortening velocity despite the lower ATPase activity of grafts refutes our hypothesis. The lower ATPase activity of SOL grafts may be attributable either to changes in myofibrillar protein composition or to the synthesis of an ATPase with a lower specific activity. Additional experiments are needed to distinguish between these possibilities.PhDAnimal PhysiologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160223/1/8422331.pd